Gas Hydrates are a form of ice crystal which contains molecular Methane (CH4) encased in the ice's molecular lattice. Methane hydrates may contain up to 160 cubic feet of gas for each cubic foot of hydrate at standard conditions.
It is well known that hydrate destabilizes to methane gas and water with addition of heat and depressurization. It is less well known that an increase of the salinity of water in equilibrium with the hydrate phase will also destabilize the hydrate. FIG. 1 displays the effect of pressure, temperature, and salinity on the methane hydrate envelope. The plot shows that the higher the temperature, the lower the pressure, and the higher the salinity, the higher likelihood of hydrate destabilization. Most proposed methods for methane production from hydrates use addition of heat or depressurization of the reservoir. However, these are energy intensive processes. At a given pressure and temperature, the alternative is to raise the salinity of the water phase in equilibrium with the hydrate.
The current method for the extraction of the hydrates comprises drilling of vertical wells for injecting of the water and for gas production. Injecting the water, warm water and/or saline water into the well and after release of the gas retrieval of the gas from the production well and its collection by the methods known in the art.
There are several configuration of the injection well and production well known in the art. U.S. Pat. No. 6,817,427 by Matsuo teaches the extraction pipe surrounding the perimeter of the injection pipe. WO 2007/117167 by Bacui, teaches wells which are vertical and parallel to each other. U.S. Pat. No. 7,165,621 by Ayoub, teaches vertical injection wells and also horizontal extraction wells. However this patent does not discuss benefits of such configurations.
All these configurations have one common deficiency: namely the well location does not provide optimal extraction of the methane from the deposit. These configurations do not address the gas which accumulates in underground cracks and pockets proximate to the wells. These configurations do not address the extraction of the gas through the entire thickness of the deposit. Most of the time in order to continuously retrieve methane from the deposit there is a requirement to drill additional wells. This procedure increases the constructing and the operational costs of the facility.
Therefore there is a need for a method of effectively extracting gas from a hydrate deposit through the whole process of recovery.
There is a need for a method of gas extracting with minimal drilling requirements.
There is a need for a process of gas extraction which promotes the growth of the depletion chamber to maximize the recovery of the hydrate from each hydrate deposit.